Buick's largest Sport Utility Vehicle,the Rainier,offers room for five and the choice of a six- or eight-cylinder engine. Every bit as plush inside as GM's full-size Sport Utility Vehicles,the Rainier's smaller size makes it a much more manageable daily driver. Most of the Rainier's mechanicals are shared with its sister vehicles,the Chevy TrailBlazer and GMC Envoy. Unique to the Rainier is the airbag rear suspension salvaged from the defunct Oldsmobile Bravada. Not only does this suspension keep the Rainier's rear end level,it provides a smoother ride than its steel-spring counterparts. The Rainier is important for Buick,as many of its upscale sedan owners also own Sport Utility Vehicles. Now,instead of turning to Lincoln or Acura,Buick owners can stay loyal to the brand.